Light emitting apparatus and control method thereof

ABSTRACT

A light emitting apparatus and a control method thereof are provided. The light emitting apparatus has a semiconductor device capable of emitting light, and the control method includes the following descriptions. A driving power of the semiconductor device is reduced to an ideal power stepwise and gradually. After every time the driving power of the semiconductor device is reduced, the semiconductor device continually emits the light by the reduced driving power within a predetermined time.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 98116399, filed on May 18, 2009. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a photoelectric apparatus and acontrol method, and more particularly, to a light emitting apparatus andthe control method.

2. Description of Related Art

The light emitting principle of the semiconductor device used foremitting light uses the special character of the semiconductor deviceand is different from the light emitting principle of the generalfluorescent lamp and the incandescent lamp. The semiconductor devicesused for emitting light have many kinds. The light emitting diode hasthe advantages of high illumination output, small volume, low drivingvoltage, and mercury free, so the light emitting diode is widely used inillumination and display apparatus area.

To make the light emitting diode be used in all kinds of products, theinstitution of rule becomes very important. Generally speaking, a rateddriving power of the light emitting diode is an important parameter todetermine the light emitting power, and when the light emitting diodeoperates, the light emitting diode is driven by the rated driving power.However, the rated driving power is not the only parameter affecting thelight emitting power of the light emitting diode. When a junctiontemperature of the light emitting diode rises, the light emitting powerof the light emitting diode reduces. Seriously, the light emitting powerof the light emitting diode with high rated driving power and highjunction temperature may be less than the light emitting power of thelight emitting diode with low rated driving power and low junctiontemperature.

For example, as shown in FIG. 1, the X-coordinate stands for theoperating time of the light emitting diode, the Y-coordinates in theleft and right sides are respectively stand for the junction temperatureand the light emitting power of the light emitting diode, curves T16 andL16 respectively stand for the characteristic curve of the lightemitting diode when the rated driving power is 1.6 watt, and curves T10and L10 respectively stand for the characteristic curve of the lightemitting diode when the rated driving power is 1 watt. The curves T16and T10 respectively stand for the relation between the junctiontemperature and the time of the light emitting diode when the rateddriving power is respectively 1.6 watt and 1 watt, and the curves L16and L10 respectively stand for the relation between the light emittingpower and the time of the light emitting diode when the rated drivingpower is respectively 1.6 watt and 1 watt.

From above, from the curves L16 and L10, when the two light emittingdiodes emit light, the light emitting power (about 301 mW) of the lightemitting diode with the rated driving power 1.6 watt is more than thelight emitting power (about 244 mW) of the light emitting diode with therated driving power 1 watt. In addition, from the curves T16 and T10,although the junction temperature of the light emitting diode with therated driving power 1.6 watt is more than the junction temperature ofthe light emitting diode with the rated driving power 1 watt, and thetemperatures of the two light emitting diodes have less differences.

However, after the above-mentioned two light emitting diodes emit thelight continuously for 6000 seconds (about 1.6 hours), the lightemitting power of the light emitting diode with the rated driving power1.6 watt has reduced to about 174 mW, and is less than the lightemitting power (about 176 mW) of the light emitting diode with the rateddriving power 1 watt. The junction temperature of the light emittingdiode with the rated driving power 1.6 watt is higher than the junctiontemperature of the light emitting diode with the rated driving power 1watt.

From the above, during the time of continuously emitting the light for6000 seconds, the light emitting diode with rated driving power 1.6 watthas bigger temperature programming than the light emitting diode withrated driving power 1 watt, so the light emitting diode with rateddriving power 1.6 watt has more power consumption and the light emittingpower is reduced as a result.

SUMMARY OF THE INVENTION

The invention provides a control method of a light emitting apparatus,and the control method may save the power consumption.

The invention provides a light emitting apparatus, and the consumingpower of the light emitting apparatus is reduced.

Other objectives and advantages may be further understood from thedisclosed technical characters of the invention.

To achieve at one of the objectives or other objectives, one embodimentof the invention provides a control method, wherein the light emittingapparatus has a semiconductor device capable of emitting light, and thecontrol method is described as following. A driving power of thesemiconductor device is reduced to an ideal power stepwise andgradually, and the semiconductor device continually emits the light bythe reduced driving power within a predetermined time after every timethe driving power of the semiconductor device is reduced.

One embodiment of the invention provides a light emitting apparatusincluding a semiconductor device and a control unit, wherein thesemiconductor device is capable of emitting light, and the control unitis electrically connected to the semiconductor device. In addition, thecontrol unit is capable of reducing a driving power of the semiconductordevice to an ideal power stepwise and gradually, wherein thesemiconductor device continually emits the light by the reduced drivingpower within a predetermined time after every time the driving power ofthe semiconductor device is reduced.

In the above-mentioned embodiment, since adopting the control method ofreducing a driving power of the semiconductor device to an ideal powerstepwise and gradually, the power consumption of the light emittingapparatus is saved.

Other objectives, features and advantages of the invention will befurther understood from the further technological features disclosed bythe embodiments of the invention wherein there are shown and describedpreferred embodiments of this invention, simply by way of illustrationof modes best suited to carry out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a diagram showing the comparing relations of the temperature,operating time, and the light emitting power of two kinds of lightemitting diodes.

FIG. 2 is a diagram showing the comparing relations of the temperature,operating time, and the light emitting power of three kinds of lightemitting diodes according to the first embodiment of the invention.

FIG. 3A is a diagram showing the comparing relations of the temperature,operating time, and the light emitting power of two kinds of lightemitting diodes according to the second embodiment of the invention.

FIG. 3B is a block diagram of a light emitting apparatus according tothe second embodiment of the invention.

FIG. 3C is a flow diagram of the control method of a light emittingapparatus according to the second embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

It is to be understood that other embodiment may be utilized andstructural changes may be made without departing from the scope of thepresent invention. Also, it is to be understood that the phraseology andterminology used herein are for the purpose of description and shouldnot be regarded as limiting. The use of “including,” “comprising,” or“having” and variations thereof herein is meant to encompass the itemslisted thereafter and equivalents thereof as well as additional items.Unless limited otherwise, the terms “connected,” “coupled,” and“mounted,” and variations thereof herein are used broadly and encompassdirect and indirect connections, couplings, and mountings.

In the embodiment, the semiconductor device used to emit light in thelight emitting apparatus may be a light emitting diode, a laser diode orother semiconductor devices capable of emitting light. In the followingembodiments, the semiconductor device used to emit light mainly uses thelight emitting diode as an example to conveniently describe, but theinvention is not to limit the following embodiments.

In consideration of the light emitting power of the light emitting diodewith high rated driving power and high junction temperature may be lessthan the light emitting power of the light emitting diode with low rateddriving power and low junction temperature, the embodiment of theinvention may reduce the power consumption of the light emitting diodethrough dynamically adjusting the driving power. The method ofdynamically adjusting the driving power is listed as follows, but theinvention is not to limit that the following embodiments are all theembodiments of the invention.

The First Embodiment

Referring to FIG. 2, curves LA and TA are the characteristic curvesaccording to dynamically adjusting the driving power of the lightemitting diode of the first embodiment of the invention, the curve LAstands for the relation between the light emitting power and the time ofthe adjusted light emitting diode, and the curve TA stands for therelation between the junction temperature and the time of the adjustedlight emitting diode. The meaning of the curves L16, T16, L10, and T10may refer to the above descriptions about FIG. 1 and is not describedhere. To be convenient for describing, in the following, the drivingpower of the light emitting diode is dynamically adjusted according tothe embodiment of the invention, and the light emitting diode is calledan object light emitting diode for short.

From above, the object light emitting diode is driven by the drivingpower 1.6 watt initiatively. From the curves LA, L16, and L10, theinitiative light emitting power of the object light emitting diode andlight emitting diode with a rated driving power 1.6 watt is about 301mW, and the value is bigger than the initiative light emitting power(about 244 mW) of the light emitting diode with a rated driving power 1watt.

Next, the driving power of the object light emitting diode is reducedstepwise and gradually, wherein the semiconductor device continuallyemits the light by the reduced driving power within a predetermined timeafter every time the driving power of the object light emitting diode isreduced. In the embodiment, the above predetermined time is 60 secondsfor example, and the driving power of the object light emitting diode isadjusted by 0.006 watt per minute, and during the 60 seconds after everytime the driving power is reduced by 0.006 watt, the object lightemitting diode continuously emits light by the reduced driving power.From the curves TA and T16, through reducing the driving power of theobject light emitting diode stepwise and gradually, the junctiontemperature of the object light emitting diode is lower than thejunction temperature of the light emitting diode driven by thecontinuously rated driving power 1.6 watt. After the object lightemitting diode continuously emits light for 6000 seconds, the drivingpower of the object light emitting diode has dropped to 1 watt, and thejunction temperature of the object light emitting diode has dropped to atemperature substantially the same as the junction temperature of thelight emitting diode with a rated driving power 1 watt.

Through the above method for reducing the driving power, a curve LAextremely similar to the curve L16 may be obtained, and the curve LAstands for that the object light emitting diode and the light emittingdiode with the rated driving power 1.6 watt has approximately the samelight emitting power in the 6000 seconds for emitting lightcontinuously. However, the consuming power of the object light emittingdiode is less than the consuming power of the light emitting diode withthe rated driving power 1.6 watt. In other words, the object lightemitting diode provides the same light emitting power with lower drivingpower and effectively reduces the consumption of the electrical energy.In addition, the junction temperature drops with the reduction of thedriving power, so the life and reliability of the light emitting diodeis improved.

The embodiment adopting stepwise and gradually reducing the drivingpower is mainly to avoid that the illumination of the light emittingdiode becomes dark obviously, and the above-mentioned method of reducingthe driving power 0.006 watt per minute is an example to describestepwise and gradually reducing the driving power, but the real reducingamplitude is determined by the product.

In the embodiment, reducing the driving power of the light emittingdiode may be achieved through reducing the driving current of the objectlight emitting diode. In more detail, if the above-mentioned objectlight emitting diode is driven by the 800 mA driving current and 1.6watt driving power initially, and the driving current of the objectlight emitting diode is reduced by 15 mA per minute in 10 minutes foremitting light continuously, the driving current and the driving powerof the object light emitting diode are respectively reduced to 650 mAand 1.16 watt after 10 minutes. The result may save 25%-30% electricalenergy comparing with the conventional light emitting diode with therated driving power 1.6 watt. However, the invention is not to limit themethod of reducing the driving power. For example, the method ofreducing the driving power of the light emitting diode may also beachieved by reducing the duty cycle of the driving voltage, drivingvoltage, and so on.

The Second Embodiment

The second embodiment is similar to the first embodiment, a safetemperature value of the semiconductor device may be further consideredwhen the second embodiment adjusts the driving power, and the finaltemperature of the semiconductor device is maintained at the safetemperature value. In addition, if the diagram of the embodiment has thesame or similar labels with the diagram of the above-mention embodiment,the labels stand for the same or similar components, and the descriptionis omitted here.

In practical use, a safe temperature value is generally set for theproduct. If a user uses the product in the environment with thetemperature exceeding the safe temperature value, the product mayproduce wrong actions and even be damaged forever, so the set of thesafe temperature value may ensure that the product operates normally.Besides adopting the concept of the first embodiment, the embodimentfurther considers the safe temperature value of the semiconductor deviceto adjust the driving power. However, the so-called safe temperaturevalue is changed with the using environment of the practical product,and the safe temperature value of the following embodiment is describedthrough some examples and is not to limit the invention.

In the embodiment, when the semiconductor device achieves the safetemperature value, the action of adjusting driving power starts. Takingthe light emitting diode as an example and referring to FIG. 3, curvesT32 and L32 stand for the characteristic curves of the light emittingdiode with the rated driving power 3.2 watt, and curves TB and LB standfor the characteristic curves of the object light emitting diode. Thecurves T32 and TB respectively stand for the relation between thejunction temperature and the time of the light emitting diode with therated driving power 3.2 watt and the object light emitting diode, andthe curves L32 and LB respectively stand for the relation between thelight emitting power and the time of the light emitting diode with therated driving power 3.2 watt and the object light emitting diode.

From above, the above-mentioned two light emitting diodes of theembodiment are driven by the driving power 3.2 watt initially, and thesafe temperature value of the object light emitting diode is set to 70°C. Before the temperature of the object light emitting reaches to 70°C., the action of reducing the driving power may not proceed. However,when the object light emitting diode continuously emits light for 1000seconds, and the temperature of the object light emitting diode achievesto 70° C., the adjustment of the driving power of the object lightemitting diode begins.

In the embodiment, the method of adjusting the driving power is toreduce the driving power to an ideal power, to further maintain thetemperature of the object light emitting diode, wherein the ideal poweris less than the rated driving power of the object light emitting diode.In the process of adjusting the driving power of the object lightemitting diode to the ideal power, the temperature of the object lightemitting diode is kept at the safe temperature value 70° C. or lowerthan 70° C. approximately. As shown by the curve TB, during the lightemitting range 1000 seconds to 4000 seconds, the final temperature ofthe object light emitting diode maintains at the safe temperature value70° C. approximately.

In other aspect, as shown by the curves T32, the light emitting diodewith the rated driving power 3.2 watt is driven at the driving power 3.2watt during the 4000 seconds continuously light emitting time all along,so the temperature of the light emitting diode with the rated drivingpower 3.2 watt rises continuously.

From the curves LB and L32, the light emitting power of the object lightemitting diode and the light emitting power of the light emitting diodewith the rated driving power 3.2 watt are close to each other, so thatthe user has difficult in feeling the differences between' the objectlight emitting diode and the light emitting diode with the rated drivingpower 3.2 watt. However, because the driving power of the object lightemitting diode needs low driving power (for example the driving power isless than the rated driving power 3.2 watt, when the temperature ishigher than the safe temperature value 70° C.)., in the practical use,the object light emitting diode may effectively save electrical energy.

The method of adjusting the driving power to the ideal power is toreduce the driving power stepwise and gradually, and the so-calledstepwise and gradually is mainly to avoid that the illumination of thelight emitting diode becomes dark obviously and make the user detect oreven feel uncomfortable. The following may further show that how theembodiment reduce the driving power of the semiconductor device to theideal power stepwise and gradually.

Please refer to FIGS. 3B and 3C, the light emitting apparatus of theembodiment includes a semiconductor device 310 used to emit light and acontrol unit 320, wherein the semiconductor device 310 used to emitlight may be a light emitting diode, a laser diode, or othersemiconductor devices capable of emitting light, and the control unit320 is electronically connected to the semiconductor device 310.

From above, first, the temperature of the semiconductor device 310 issensed (step S301), in the embodiment, for example, a sensing unit 330electrically connected to the control unit 320 in the light emittingapparatus 300 is set to sense the semiconductor device 310 and get thetemperature of the semiconductor device 310.

In the embodiment, the sensing unit 330 is a thermistor. The thermistorsenses the temperature information of the semiconductor device 310directly. However, in other embodiments, the temperature information ofthe semiconductor devices 310 may also be got through the relation ofthe junction temperature, light emitting efficiency, and the drivingpower of the semiconductor device 310. For example, the sensing unit 330may be a photo-sensor to sense the light emitting power of thesemiconductor device 310, then the control unit 320 further gets thetemperature of the semiconductor device 310 according to the lightemitting power of the semiconductor device 310 sensed by the sensingunit 330 and the driving power of the semiconductor device 310 (stepS301).

Then, the temperature of the semiconductor device 310 is compared withthe safe temperature value as a reference of the following action ofadjusting the driving power. Taking the 70° C. safe temperature value asan example, the control unit 320 of the embodiment may first determinesif the temperature of the semiconductor device 310 is higher than the70° C. safe temperature value (step S303), to ensure that thetemperature of the semiconductor device 310 is substantially higher thanthe 70° C. safe temperature value before every time reducing the drivingpower. This action may avoid that the control unit 320 reduces thetemperature of the semiconductor device 310 excessively.

When the above-mentioned judging result is that the temperature of thesemiconductor device 310 is higher than the 70° C. safe temperaturevalue, the control unit 320 may reduce the driving power of thesemiconductor device 310 according to the result (step S305). In thisway, the semiconductor device 310 may emit light according to thereduced driving power.

Then, the control unit 320 determines the variation of the temperatureof the semiconductor device 310 in a predetermined time, and the resultis the reference of whether adjusting the driving power again or not,wherein the semiconductor device 310 emits light by the reduced drivingpower in a predetermined time. In more detail, suppose the predeterminedtime to be 1 minute, and the control unit 320 may determine whether thetemperature of the semiconductor device 310 rises in 1 minute (stepS307). If the temperature rises, the above-mentioned reduced drivingpower is still too high, so the step S305 is proceeded again, in otherwords, the control unit 320 reduces the driving power of thesemiconductor device 310 again.

In addition, the control unit 320 may also determine if the temperatureof the semiconductor device 310 decreases in 1 minute (step S309). Ifthe temperature decreases, and the temperature of the semiconductordevice 310 is lower than the 70° C. safe temperature value after 1minute predetermined time, the above-mentioned reduced driving power istoo low, so the step S301 is proceeded again to sense the temperature ofthe semiconductor device 310 and the light emitting power, to make theadjustment of the driving power be more accurate.

In other aspect, if the control unit 320 determines that the temperatureof the semiconductor device 310 decreases in 1 minute, and thetemperature of the semiconductor device 310 is still higher than the 70°C. safe temperature value after 1 minute predetermined time, the controlunit 320 determines if the variation amplitude of the temperature of thesemiconductor device 310 is higher than a predetermined value in 1minute predetermined time (step S311) as a reference to decide whetherto adjust the driving power again. The step may avoid that the controlunit 320 reduces the temperature of the semiconductor devices 310excessively.

From above, suppose the above-mentioned predetermined value is 3° C.When the control unit 320 determines that the variation amplitude of thetemperature of the semiconductor device 310 is higher than 3° C.predetermined value in 1 minute predetermined time, the result means thedriving power of the semiconductor device 310 has not reduced to theideal power, so the step S305 is proceeded again to further make thecontrol unit 320 adjust the driving power of the semiconductor device310. If the variation amplitude of the temperature device 310 is higherthan 3° C. and the temperature of the semiconductor device 310 decreasesbelow the 70° C. safe temperature value, the step S305 is proceededagain to further make the control unit 320 increase the driving power ofthe semiconductor device 310; or if the variation amplitude of thetemperature device 310 is higher than 3° C. and the temperature of thesemiconductor device 310 is still higher than the 70° C. safetemperature value, the step S305 is proceeded again to further make thecontrol unit 320 decrease the driving power of the semiconductor device310. Contrarily, if the control unit 320 determines that the variationamplitude of the temperature of the semiconductor device 310 is nothigher than 3° C. predetermined value in 1 minute predetermined time,the result means the driving power of the semiconductor device 310 hasreduced to the ideal power (step S313), and the temperature of thesemiconductor device 310 is the safe temperature value higher or lower.

After that, the control unit 320 may still proceed the step S311continuously, that is to determine if the variation amplitude of thetemperature of the semiconductor device 310 is higher than 3° C.predetermined value in 1 minute predetermined time to ensure thetemperature of the semiconductor device 310 maintain at the safetemperature value.

The above-mentioned steps S305, S307, S309, S311, and S313 are adjustedand determined according to the temperature of the semiconductor device310 mainly. However, because the relations of the junction temperature,light emitting power, and the driving power of the semiconductor device310 are depended on each other, in other embodiments, the steps S305,S307, S309, S311, and S313 may also be adjusted and determined accordingto the light emitting power (that is illumination) of the semiconductordevice 310.

From above, the embodiment not only has the advantages of the firstembodiment, but also further takes consideration of the safe temperaturevalue of the semiconductor device to make the light emitting apparatususing the semiconductor device have more stable light emittingillumination and higher level safety specialist.

In summary, the embodiment or embodiments of the invention may have atleast one of the following advantages: the control method of the lightemitting apparatus includes reducing the driving power of thesemiconductor device in the light emitting apparatus to the ideal powerstepwise and gradually, to make the light emitting apparatus have theadvantages of low power consumption, long service life, highreliability, and high level safety specialist.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform or to exemplary embodiments disclosed. Accordingly, the foregoingdescription should be regarded as illustrative rather than restrictive.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. The embodiments are chosen anddescribed in order to best explain the principles of the invention andits best mode practical application, thereby to enable persons skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use orimplementation contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and their equivalentsin which all terms are meant in their broadest reasonable sense unlessotherwise indicated. Therefore, the term “the invention”, “theinvention” or the like does not necessarily limit the claim scope to aspecific embodiment, and the reference to particularly preferredexemplary embodiments of the invention does not imply a limitation onthe invention, and no such limitation is to be inferred. The inventionis limited only by the spirit and scope of the appended claims. Theabstract of the disclosure is provided to comply with the rulesrequiring an abstract, which will allow a searcher to quickly ascertainthe subject matter of the technical disclosure of any patent issued fromthis disclosure. It is submitted with the understanding that it will notbe used to interpret or limit the scope or meaning of the claims. Anyadvantages and benefits described may not apply to all embodiments ofthe invention. It should be appreciated that variations may be made inthe embodiments described by persons skilled in the art withoutdeparting from the scope of the invention as defined by the followingclaims. Moreover, no element and component in the disclosure is intendedto be dedicated to the public regardless of whether the element orcomponent is explicitly recited in the following claims.

1. A control method of a light emitting apparatus, the light emittingapparatus having a semiconductor device capable of emitting light, thecontrol method comprising the following step: reducing a driving powerof the semiconductor device to an ideal power stepwise and gradually,wherein the semiconductor device continually emits the light by thereduced driving power within a predetermined time after every time thedriving power of the semiconductor device is reduced.
 2. The controlmethod as claimed in claim 1, further comprising: sensing a temperatureof the semiconductor device; comparing the temperature of thesemiconductor device with a safe temperature value, wherein thetemperature of the semiconductor device is higher than the safetemperature value before every time reducing the driving power.
 3. Thecontrol method as claimed in claim 2, wherein the step of reducing thedriving power of the semiconductor device to the ideal power stepwiseand gradually comprises: determining whether the temperature ofsemiconductor device increases in the predetermined time after everytime reducing the driving power; and reducing the drive power if thetemperature of the semiconductor device increases in the predeterminedtime.
 4. The control method as claimed in claim 2, wherein the step ofreducing the driving power of the semiconductor device to the idealpower stepwise and gradually comprises: determining whether thetemperature of the semiconductor device decreases in the predeterminedtime after every time reducing the driving power; determining whether anamount of a variation of the temperature of the semiconductor device ishigher than a predetermined value if the temperature of thesemiconductor device decreases in the predetermined time and thetemperature of the semiconductor device is still higher than the safetemperature value after the predetermined time; and adjusting thedriving power of the semiconductor device if the amount of the variationof the temperature of the semiconductor device is higher than thepredetermined value in the predetermined time.
 5. The control method asclaimed in claim 4, wherein the step of reducing the driving power ofthe semiconductor device to the ideal power stepwise and graduallyfurther comprises: sensing the temperature of the semiconductor deviceif the temperature of the semiconductor device decreases in thepredetermined time and the temperature of the semiconductor device islower than the safe temperature value after the predetermined time. 6.The control method as claimed in claim 1, further comprising: sensing alight emitting power of the semiconductor device; getting a temperatureof the semiconductor device according to the driving power of thesemiconductor device and the light emitting power sensed by thesemiconductor device; and comparing the temperature of the semiconductordevice with a safe temperature value, wherein the temperature of thesemiconductor device is higher than the safe temperature value beforeevery time reducing the driving power.
 7. The control method as claimedin claim 6, wherein the step of reducing the driving power of thesemiconductor device to the ideal power stepwise and graduallycomprises: determining whether the temperature of semiconductor deviceincreases in the predetermined time after every time reducing thedriving power; and reducing the drive power if the temperature of thesemiconductor device increases in the predetermined time.
 8. The controlmethod as claimed in claim 6, wherein the step of reducing the drivingpower of the semiconductor device to the ideal power stepwise andgradually comprises: determining whether the temperature ofsemiconductor device decreases in the predetermined time after everytime reducing the driving power; determining whether an amount of avariation of the temperature of the semiconductor device is higher thana predetermined value if the temperature of the semiconductor devicedecreases in the predetermined time and the temperature of thesemiconductor device is higher than the safe temperature value after thepredetermined time; and adjusting the driving power of the semiconductordevice if the amount of the variation of the temperature of thesemiconductor device is higher than the predetermined value in thepredetermined time.
 9. The control method as claimed in claim 8, whereinthe step of reducing the driving power of the semiconductor device tothe ideal power stepwise and gradually further comprises: sensing thetemperature of the semiconductor device if the temperature of thesemiconductor device decreases in the predetermined time and thetemperature of the semiconductor device is lower than the safetemperature value after the predetermined time.
 10. The control methodas claimed in claim 1, wherein the driving power of the semiconductordevice is reduced through reducing a driving circuit of thesemiconductor device.
 11. The control method as claimed in claim 1,wherein the ideal power is less than a rated driving power of thesemiconductor device.
 12. A light emitting apparatus, comprising: asemiconductor device, capable of emitting light; and a control unit,electrically connected to the semiconductor device and capable ofreducing a driving power of the semiconductor device to an ideal powerstepwise and gradually, wherein the semiconductor device continuallyemits the light by the reduced driving power within a predetermined timeafter every time the driving power of the semiconductor device isreduced.
 13. The light emitting apparatus as claimed in claim 12,further comprising a sensing unit electrically connected to the controlunit to sense a temperature of the semiconductor device; wherein thecontrol unit compares the temperature of the semiconductor device with asafe temperature value and the temperature of the semiconductor deviceis higher than the safe temperature value before every time reducing thedriving power.
 14. The light emitting apparatus as claimed in claim 13,wherein the control unit determines whether the temperature ofsemiconductor device increases in the predetermined time after everytime reducing the driving power, and the control unit reduces the drivepower if the temperature of the semiconductor device increases in thepredetermined time.
 15. The light emitting apparatus as claimed in claim13, wherein the control unit determines whether the temperature of thesemiconductor device decreases in the predetermined time after everytime reducing the driving power, the control unit determines whether anamount of a variation of the temperature of the semiconductor device ishigher than a predetermined value if the temperature of thesemiconductor device decreases in the predetermined time and thetemperature of the semiconductor device is still higher than the safetemperature value after the predetermined time, and the control unitadjusts the driving power of the semiconductor device if the amount ofthe variation of the temperature of the semiconductor device is higherthan the predetermined value in the predetermined time.
 16. The lightemitting apparatus as claimed in claim 12, further comprising a lightsensing unit electrically connected to the control unit to sense a lightemitting power of the semiconductor device, wherein the control unitgets the temperature of the semiconductor device according to thedriving power of the semiconductor device and the light emitting powersensed by the semiconductor device, the control unit compares thetemperature of the semiconductor device with a safe temperature value,and the temperature of the semiconductor device is higher than the safetemperature value before every time reducing the driving power.
 17. Thelight emitting apparatus as claimed in claim 16, wherein the controlunit determines whether the temperature of semiconductor deviceincreases in the predetermined time after every time reducing thedriving power, and the control unit reduces the drive power if thetemperature of the semiconductor device increases in the predeterminedtime.
 18. The light emitting apparatus as claimed in claim 16, whereinthe control unit determines whether the temperature of the semiconductordevice decreases in the predetermined time after every time reducing thedriving power, the control unit determines whether an amount of avariation of the temperature of the semiconductor device is higher thana predetermined value if the temperature of the semiconductor devicedecreases in the predetermined time and the temperature of thesemiconductor device is higher than the safe temperature value after thepredetermined time, and the control unit adjusts the driving power ofthe semiconductor device if the amount of the variation of thetemperature of the semiconductor device is higher than the predeterminedvalue in the predetermined time.
 19. The light emitting apparatus asclaimed in claim 12, wherein the control unit reduces the driving powerof the semiconductor device through reducing a driving circuit of thesemiconductor device.
 20. The light emitting apparatus as claimed inclaim 12, wherein the ideal power is less than a rated driving power ofthe semiconductor device.